Caulking a stucco house: what goes in the joints, and what never gets caulked

Every October somebody calls me holding a caulking gun and asking what to load into it. Fair question, and the answer saves more walls than any product does: caulk for stucco belongs in the joints where the stucco meets something else, a window frame, a door, a vent, a run of stone. It does not belong in the wall itself. After 25-plus years on GTA houses, most of the sealant trouble I get called for is the right tube squeezed into the wrong gap.

Below is how to tell a joint from a crack, where on the house a bead earns its keep, the four spots where caulk does real harm, which kind to buy, and what a bead that survives a few Januaries looks like when you slice through it.

Should you caulk a crack in stucco?

Not as the repair. A crack in the open face of the wall means the stucco itself broke, from settling, shrinkage or water freezing behind it, and caulk on top only hides that. It gets routed, meshed and refinished. Caulk is for joints, the lines where stucco stops against a different material that moves on its own schedule.

The grey zone is the hairline right at a window corner. A sound hairline there can take a sealant made to be painted until the wall gets a proper refinish, and I have no quarrel with a homeowner doing that for a season. A corner crack you can fit a coin into, or one with a stain under it, is past the caulk stage. The price lines for real crack work are on the stucco repair page: a routed and meshed crack runs $120 to $400.

Where sealant belongs on a stucco house

Walk the house in this order and look at each kind of joint. The ages in the tags are how long original builder sealant usually lasts at each one before it needs cutting out and redoing.

1. Around every window and door frame, sides and head. This is the longest run on most houses and the one that leaks into a room when it goes. 10 to 15 yrs
2. Where stucco meets brick, stone veneer or siding. It shows as a dead-straight vertical line, usually at an outside corner or under a bay window. 10 to 15 yrs
3. Around anything poking through: dryer and furnace vents, the gas line, hose bibs, cable and AC lines, light fixtures. Small joints, but there are a lot of them. about 10 yrs
4. Expansion and control joints, where the wall was designed to move. Not every system seals these, so check what kind you have first; I go through them in the post on stucco control joints. 15 to 20 yrs

On a lot of the 1990s houses around Erin Mills and Bronte the original beads are all the same age, so they tend to give up together. If one window has a split bead, look at the rest before you buy one tube.

Four places a bead of caulk does damage

A stucco wall is built to let some water out on purpose. Seal the exits and you keep that water inside. These are the gaps I most often find caulked shut by someone trying to help:

• The gap along the bottom of the wall, at the metal weep screed a few inches above the soil or the paving. Water that gets behind the stucco drains out here. There is more on keeping it open in the guide to clearance at grade.
• The little slots on the bottom face of a vinyl or aluminium window frame. Those are the window's own drains, and a neat bead across them turns the frame into a bathtub.
• The lower, outward edge of the metal flashing over a window or door head, and the end of a kick-out flashing at a roofline. Seal the top of a flashing to the wall if the detail calls for it, never the drip edge where the water leaves. Flashing, explained for homeowners shows which edge is which.
• Over the finish coat of an EIFS wall. Acrylic finish softens a little when it stays wet, and a sealant stuck to it can pull the finish off the base coat underneath when the joint opens up in the cold. On foam walls the bead belongs on the base coat, with the finish kept out of the joint.

That last point is not my opinion. Sika's technical bulletin on sealant joint repair in EIFS tells installers to clean any finish out of the joint, coat the joint faces with base coat where needed, use closed-cell backer rod, and never trowel finish into or over the sealant.

Which caulk is best for stucco?

For joints that move, a polyurethane or hybrid sealant rated for exterior masonry. It stretches with the joint, sticks to cement and stone, and takes paint. Against glass, aluminium or vinyl, silicone grips best but will not take paint. Plain acrylic latex suits only still, narrow gaps on an outside wall.

That split, urethane where the joint gets painted and silicone against glass and metal, is the same one written into our exterior caulking work, with the colour matched to the wall. Whatever you pick, read two lines on the tube before you buy it: the minimum application temperature, and whether the maker lists masonry or EIFS among the surfaces. If the tube does not mention either, it is a bathroom product.

What a bead that lasts looks like

A sealant joint that survives is thin, even, stuck on two sides only, and sitting on a foam rod. Most failed beads I cut out fail one of those four tests.

The backer rod is the part homeowners skip, and it matters more than the brand. Without it the sealant fills the whole gap and sticks to the back as well as both sides. Stuck on three sides, it cannot stretch, so the first hard freeze tears it off one edge. A fat bead is not a stronger bead. A slim one with a rod behind it outlasts it.

Tooling counts too. Pressing the wet bead with a spatula pushes it against both faces and gives it that slightly hollow shape. A finger dipped in soapy water looks tidy and leaves soap where the bond should be.

Can you caulk stucco in late fall?

Yes, if the joint is dry and the air is above the minimum printed on the tube, which for many sealants sits a few degrees above freezing. In a GTA October that means afternoons, the sunny side first, nothing after rain, and stopping before the evening damp settles. Frost in a joint ruins the bond.

Fall is actually the time I like best for this work. A bead set at middle-of-the-year temperatures sits halfway between its summer squeeze and its winter stretch, and the wall goes into freeze-up closed. In Port Credit and along the lake the shaded north walls can stay damp all day in November, so check them with your hand before you start, not by the forecast.

Why caulk over old caulk fails

New sealant does not bond reliably to old, failed sealant. A bead run over the top looks great in the photos and lets go along the same line it covered, often the first winter. The old bead has to come out completely, down to clean edges on both sides, before a new rod and bead go in.

This is the classic $99 patch-and-pray job: one tube of white, a fast bead over everything, gone by lunch. It hides the split you could see and keeps the water you could not, and by March the joint is open again with a fresh line of dirt along it.

What recaulking a stucco house costs

Our sealant renewal at windows, doors and joints runs $6 to $12 per linear foot, and a whole-house renewal lands between $800 and $2,500 on most homes. The spread comes from how many windows there are, how long the joints are in total and how high the work goes.

The receipt above is the arithmetic on a typical two-storey: eight windows at about 16 feet of joint each, two doors, the vents and lines, and one stone-to-stucco corner, 208 feet in all. A bungalow with five windows comes in far lower; a house with a third storey and a lot of stone comes in near the top of the range. If a joint has already let water in and the stucco beside it is soft, that section is a repair rather than a bead, and it gets priced separately.

If you are not sure whether the line on your wall is a joint or a crack, send a close-up and a photo of the whole wall through the contact page, or call (905) 973-6470. I usually get back to people within a day, and you get a fixed written quote at no charge.